1. Field of Invention
Aspects of this invention are related to endoscopic imaging and are more particularly related to simultaneously focusing visible light images and near infrared or ultraviolet images.
2. Related Art
The da Vinci® Surgical System, commercialized by Intuitive Surgical, Inc., Sunnyvale, Calif., is a minimally invasive teleoperated surgical system that offers patients many benefits, such as reduced trauma to the body, faster recovery and shorter hospital stay. One key component of the da Vinci® Surgical System is a capability to provide two-channel (i.e., left and right) video capture and display of visible images to provide stereoscopic viewing for the surgeon.
Such electronic stereoscopic imaging systems may output high definition video images to the surgeon, and may allow features such as zoom to provide a “magnified” view that allows the surgeon to identify specific tissue types and characteristics, as well as to work with increased precision. In a typical surgical field, however, certain tissue types are difficult to identify, or tissue of interest may be at least partially obscured by other tissue. This complicates the surgical procedure.
In some applications, fluorescence images in the near infrared spectrum and reflected white light images are used in minimally invasive surgery. But, the back focal distance for a near infrared fluorescence image is different from the back focal distance for a reflected white light image. Thus, when switching from one mode of operation or the other a focus adjustment is required. When both a near infrared fluorescence image and a reflected white light image are being viewed simultaneously, the typical optics in an endoscope and camera do not provide simultaneous focus of both images. A similar situation may also occur in the ultraviolet spectrum.
One solution to the differences in focal plane for different wavelength images is presented in International Publication Number WO 2010/042522A1 published 15 Apr. 2010. This approach utilizes a prism including sections made of different materials having different indices of refraction. A dichroic coating is placed on the diagonal surface between the sections so that one half of the diagonal surface is coated with a short pass coating that transmits visible light and reflects near infrared light. The other half of the diagonal surface is coated with a long pass coating that transmits near infrared light and reflects visible light.
This approach works for small differences in focus. However, this approach is not practical for larger differences in focus because the size of the prism required becomes too great. This approach also requires a physically larger camera as the imaging path becomes offset laterally by some amount resulting in a larger camera assembly. This approach also requires finding two materials with exactly the “correct” indexes and Abbe numbers to satisfy the design. There are a limited number of suitable materials so a solution may not be possible. This approach also cannot correct more general optical aberrations.